<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>上划线、中划线、下划线</title>
</head>
<body>
  <canvas id="c1" width="300" height="300" style="border: 1px solid #ccc"></canvas>

  <!-- <button>上划线</button> -->
  <button onclick="linethrough()">中划线</button>
  <!-- <button>下划线</button> -->
  <canvas id="c2" width="300" height="300" style="border: 1px solid #ccc"></canvas>

  <script src="../../script/fabric.js"></script>
  <script>
    // c1
    const canvas1 = new fabric.Canvas('c1')

    const iText1 = new fabric.IText('aaa',{
      styles: {
        0: {
          0: { overline: true }, // 上划线
          1: { linethrough: true }, // 中划线
          2: { underline: true } // 下划线
        }
      }
    })

    canvas1.add(iText1)


    // c2
    const canvas2 = new fabric.Canvas('c2')

    const iText2 = new fabric.IText('hello wor\nld')

    canvas2.add(iText2)

    function linethrough() {
      let activeTxt = canvas2.getActiveObject()

      if (!activeTxt) return

      if (activeTxt.isEditing) {
        // 编辑状态
        const state = activeTxt.getSelectionStyles().find(item => item.linethrough !== true)

        if (!state || (JSON.stringify(state) === '{}' && activeTxt['linethrough'] === true)) {
          activeTxt.setSelectionStyles({ 'linethrough': false })
        } else {
          activeTxt.setSelectionStyles({ 'linethrough': true })
        }
      } else {
        // 选择状态
        if (activeTxt['linethrough'] === true) {
          activeTxt.linethrough = false
          activeTxt.dirty = true;
          let s = activeTxt.styles
          for(let i in s) {
            for (let j in s[i]) {
              s[i][j].linethrough = false
            }
          }
        } else {
          activeTxt.linethrough = true
          activeTxt.dirty = true;
          let s = activeTxt.styles
          for(let i in s) {
            for (let j in s[i]) {
              s[i][j].linethrough = true
            }
          }
        }
      }

      canvas2.renderAll()
    }

  </script>
</body>
</html>